1. Field of the Invention
The present invention relates to a lead frame conveying method and conveying apparatus in which lead frames supplied from a loader side magazine are chucked and conveyed by the feeding claws of a frame feeder installed in a bonding apparatus such as a wire bonding apparatus, die bonding apparatus, etc.
2. Prior Art
FIG. 3 shows a conventional bonding apparatus A frame feeder 3 which conveys lead frames 1 includes guide rails 4 that are provided with guide grooves 4a for guiding the lead frames 1; and the feeder 3 further includes loader side feeding claws 5 and unloader side feeding claws 6.
The loader side feeding claws 5 consist of a pair of claws (an upper claw 5a and a lower claw 5b), and the unloader side feeding claws 6 consist of a pair of claws (an upper claw 6b and a lower claw 6b). Furthermore, the loader side and unloader side feeding claws 5 and 6 are opened and closed by a claw opening-and-closing means (not shown) and are moved along the guide rails 4 by a claw moving means (not shown).
Examples of frame feeders 3 of this type are disclosed in Japanese Patent Application Publication (Kokoku) No. 63-56122 and Japanese Patent Application Laid-Open (Kokai) No. 4-346446.
A bonding apparatus 10 such as a wire bonding apparatus, die bonding apparatus, etc., is installed so as to face the bonding position 7 which is located on one side of the guide rails 4 of the frame feeder 3. This bonding apparatus 10 has an XY table 11 which is driven in the X and Y directions; and a bonding head 12 is mounted on this XY table 11, and a camera holder 14 to which a television camera 13 is attached is fastened to this bonding head 12. Furthermore, a bonding arm 16 to which a bonding tool 15 is attached is installed on the bonding head 12 so that the bonding arm 16 can be raised and lowered. The television camera 13 is positioned above the bonding position 7, and the bonding tool 15 is provided so as to be offset from the television camera 13 by a distance of Y1. The bonding arm 16 is raised and lowered by a Z (vertical) driving motor (not shown).
The bonding apparatus described in Japanese Patent Application Kokai No. 5-275502 is an example of a bonding apparatus 10 of this type.
A loader side magazine 20A and an unloader side magazine 20B, which store lead frames therein, are installed at both ends of the guide rails 4. The loader side and unloader side magazines 20A and 20B are respectively positioned and carried on magazine holders 22 which are raised and lowered by a loader side elevator device 21A and an unloader side elevator device 21B. The lead frames 1 inside the loader side magazine 20A are pushed out into the guide grooves 4a of the guide rails 4 by a frame pusher 23.
Examples of systems equipped with elevator devices 21A and 21B of this type are disclosed in Japanese Patent Application Publication (Kokoku) Nos. S63-56122, H1-32127 and H2-4486.
In FIG. 3, the reference numeral 24 indicates a photo sensor which detects the lead frames 1 pushed out by the frame pusher 23.
An outline of the feeding operation of the above conventional frame feeder will be described with reference to FIG. 4.
A plurality of semiconductor chips (five chips in the shown embodiment, and which are hereafter referred to as "IC's") 2A through 2E are mounted on each of the lead frames 1A, 1B . . . shown in FIG. 4.
Beginning in the state shown in FIG. 4(a), the frame pusher 23 (see FIG. 3(b)) performs a push-out operation which pushes out the lead frame 1A at a low speed until the lead frame 1A is detected by the photo sensor 24. In this case, the loader side feeding claws 5 are in an open state, and the position where the loader side feeding claws 5 are located at this point is the feeding claw starting point A. When the photo sensor 24 detects the lead frame 1A, the low-speed push-out operation of the frame pusher 23 is ended.
Next, the frame pusher 23 pushes the lead frame 1A out to the position shown in FIG. 4(b), where the lead frame 1A can be chucked by the loader side feeding claws 5. Then, the loader side feeding claws 5 close and chuck the lead frame 2A; and, as shown in FIG. 1(c), the loader side feeding claws 5 feed the lead frame 1A to a calculated initial alignment position in order to perform an initial alignment (positioning).
Then, an initial alignment operation (which will be described next) is performed. This initial alignment operation is, in the shown embodiment, performed by the frame feeder described in Japanese Patent Application Publication (Kokoku) No. S63-56122.
More specifically, the loader side feeding claws 5 open so as to release the lead frame 1A, and then the loader side feeding claws 5 move slightly in the direction of arrow 30 as shown in FIG. 4(d). At this time, the right-side ends of the loader side feeding claws 5 are positioned at point B.
Next, after the loader side feeding claws 5 close, they are moved in the direction of arrow 31, so that the leading end of the lead frame 1A is pushed back by the loader side feeding claws 5, thus aligning the leading end of the lead frame 1A as shown in FIG. 4(e). Then, the loader side feeding claws 5 again move slightly in the direction of arrow 32 and Open so that the loader side feeding claws 5 will not interfere with the lead frame 1A. Afterward, the loader side feeding claws 5 move in the direction of arrow 33 and return to the feeding claw starting point A as shown in FIG. 4(f).
Next, a single-pitch feeding operation which feeds the lead frame 1A is performed. More specifically, the loader side feeding claws 5 close and chuck the lead frame 1A and then perform a feeding operation corresponding to one pitch as shown in FIG. 4(g). The loader side feeding claws 5 then open and return to the feeding claw starting point A as shown in FIG. 4(h); and then, the loader side feeding claws 5 close and chuck the lead frame 1A so as to perform a feeding operation until the first IC 2A on the lead frame 1A reaches the bonding position 7 as shown in FIG. 4(i). Following the completion of this feeding operation, the lead frame 1A is clamped by a window damper (not shown). In this state, the bonding points on the IC 2A are detected by the television camera 13 shown in FIG. 3, and bonding is performed on the corrected bonding points by the bonding tool 15 of the bonding apparatus 10. Meanwhile, the loader side feeding claws 5 return to the feeding claw starting point A as shown in FIG. 4(j).
After bonding on the IC 2A is completed, the window damper opens; and an operation which feeds the IC 2B to the bonding position 7 is performed by the loader side feeding claws 5. More specifically, in the state shown in FIG. 4(j), the loader side feeding claws 5 close and chuck the lead frame 1A and then perform a feeding operation corresponding to one IC pitch as shown in FIG. 4(k). Afterward, the lead frame 1A is clamped by the window damper in the same fashion as described above, and bonding is performed on the IC 2B; and then, the unloader side feeding claws 5 return to the feeding claw starting point A in an open state as shown in FIG. 4(1). Next, a feeding operation similar to the feeding operation on the IC 2B is performed so that the IC 2C is fed to the bonding position 7 as shown in FIG. 4(m), and bonding is performed on the IC 2C by the same operation as that described above.
Although not mentioned above, the unloader side feeding claws 6 perform the same actions as the loader side feeding claws 5 when the loader side feeding claws 5 feed the lead frame 1A by opening and closing and performing reciprocating motions.
As shown in FIG. 4(n), the loader side feeding claws 5 being opened return to the feeding claw starting point A. At this point, the trailing end of the lead frame 1A is positioned on the bonding position 7 side of the feeding claw starting point A. In addition, the unloader side feeding claws 6 are opened so that these claws can chuck the lead frame 1A. While bonding is being performed on the IC 2C, the next lead frame 1B is fed to a position which allows the lead frame 1B to be chucked by the loader side feeding claws 5, as shown in FIG. 4(o). This operation is the same as the operation shown in FIGS. 4(a) and 4(b).
When bonding on the IC 2C is completed and the window damper opens, the unloader side feeding claws 6 close and chuck the lead frame 1A, so that the IC 2D on the lead frame 1A is fed to the bonding position 7 as shown in FIG. 4(p). In this case, since the trailing end of the lead frame 1A has not passed point B, no feeding of the lead frame 1B is performed by the loader side feeding claws 5. This feeding of the lead frame 1B is delayed in order to prevent the lead frame 1B from interfering with the preceding lead frame 1A. In other words, the loader side feeding claws 5 perform a reciprocating movement while in an open state. Once the trailing end of the lead frame 1A has passed point B, conveying of the lead frame 1B becomes possible; and the operation shown in FIG. 4(b) and subsequent steps are performed on the lead frame 1B. As shown in FIG. 4(q), the unloader side feeding claws 6 return to the starting point of the feeding claws 6 in an open state; and when the bonding on the IC 2D is completed, the unloader side feeding claws 6 perform an operation which feeds the IC 2E to the bonding position 7. Subsequently, the IC's 2A, 2B . . . of the lead frame 1B are successively fed to the bonding position 7, and bonding operations are performed on each IC.
Thus, the leading end surface of each lead frame 1 supplied from the loader side magazine 20A is pushed by the end surfaces of the loader side feeding claws 5 so that the lead frame 1 is positioned (aligned). Afterward, the lead frame is conveyed to the bonding position with the loader side feeding claws 5 changing their grip on the lead frame 1 several times by opening and closing.
In the method described above, the positioning of the lead frames 1 is accomplished by pushing the lead frames 1 with the end surfaces of the loader side feeding claws 5, a long-term use wears out the loader side feeding claws 5 as at 35 in FIG. 5, generating a positional discrepancy during positioning.
Furthermore, wide lead frames 1 tend to sag as shown in FIG. 6(a); dimensional errors between individual loader side magazines 20A and looseness between the loader side magazine 20A and the magazine holder holding the loader side magazine 20A cause the lead frames 1 to deform as shown in FIG. 6(c); and looseness of the guide rails 4 in the direction of width and differences in the width adjustment of the guide rails 4 cause the lead frames to deform. Because of these problems, the lead frames 1 may contact the end surfaces 8a or 8b of the loader side feeding claws 5 as shown in FIGS. 6(a) and 6(b), and it becomes uncertain exactly where the lead frames 1 will contact the end surfaces of the loader slide feeding claws 5; and as a result, positional discrepancies are generated during the positioning of the lead frames 1.
In addition, as shown in FIG. 6(d), since the portion of the end surface of each lead frame 1 contacted by the end surfaces of the loader side feeding claws 5 may be uncertain, depending on the shape of the end surface of the lead frame 1, positional discrepancies are likely to be generated.
In FIGS. 6(c) and 6(d), the two-dot chain lines indicate normal conditions, while the solid lines indicate abnormal conditions.
Furthermore, after each lead frame 1 has been positioned, the lead frame 1 is conveyed to the bonding position 7 while being repeatedly gripped by the loader side feeding claws 5. As result, because of deformation of the lead frame 1 as described above with reference to FIG. 6, as well as deformation of the lead frame 1 caused by the heat of the heater which heats the lead frame 1, and deformation of the lead frame 1 caused by expansion, etc., a positional discrepancy C as shown in FIG. 7(b) is generated in the leading end of the lead frame 1 each time the lead frame 1 is gripped by the loader side feeding claws 5, if the loader side feeding claws 5 are closed under conditions such as those shown in FIG. 7(a). As a result, a lead frame feeding discrepancy is generated while the lead frame 1 is being conveyed to the bonding position 7.